1-to-N collation is a method for collating a plurality of registered data items, which are registered in a data base or the like in advance, with newly provided input data, and extracting registered data matching the input data. The 1-to-N collation is used for a biometric authentication system, for example, which collates such biometric data as a vein pattern of a palm or finger prints so as to authenticate a person.
In a biometric authentication system using the 1-to-N collation, input data and registered data are collated respectively, and similarities of the registered data to the input data are calculated. A threshold is set for similarities. In the biometric authentication system, registered data of which similarity is higher than the threshold is used to authenticate a person, which is a measurement subject of the input data.
In such a biometric authentication system, the generation of an authentication error, that is, recognizing input data of an unregistered person as data of a registered person, need to be prevented in terms of security.
One of the available technologies to control authentication errors, there is a technology to adjust the threshold of similarity depending on the situation (Technology 1). For example, if reliability of collation between input data and registered data is low, authentication conditions based on the threshold of similarity are set to be more strict. If the authentication conditions based on the threshold are set to be strict (e.g. setting high threshold), the generation of an authentication error is controlled. However, if an individual not familiar to the system is authenticated and data measurement accuracy drops, for example, the difference between the input data and registered data of this person increases, and similarity decreases. If the similarity decreases, although this person is a registered person, the case that the person is determined to be an unregistered person and is not authenticated is happened, because the threshold is set too high. In this case, this person to be authenticated needs to be measured again by a measurement apparatus, and authentication takes time. This means that convenience may drop if Technology 1, which adjusts the threshold depending on the situation, is used.
Another available technology to control authentication errors is a technology to improve reliability using other authentication methods as well (Technology 2). Other authentication methods include password authentication and biometric authentication using other portions of a biological body. However equipment and operations to support the other authentication methods are required, and convenience and processing speed may drop. In the case of requiring equipment, an increase in cost and installation locations could be problematic.    Therefore according to prior art, authentication errors may be controlled, but convenience could diminish.    [Patent document 1] Japanese Patent Application Laid-Open No. 2004-78686    [Patent document 2] Japanese Patent Application Laid-Open No. 2000-215316    [Patent document 3] Japanese Patent Application Laid-Open No. 2003-346149